| 摘要 |
<P>PROBLEM TO BE SOLVED: To record and reproduce information satisfactorily with the same RIM strength and without any loss of light quantity in the case of either of two optical recording media with different numerical apertures and different substrate thickness. <P>SOLUTION: An expander optical system 114 of a magnification converting means is composed of two lenses being lenses 114a and 114b and changes an interval between the lenses as to whether to record and reproduce an optical recording medium (BD) or an optical recording medium (HD). A liquid crystal aperture limiting element performs switching as to whether to perform aperture limitation or blind transmission in accordance with a medium. Although NA0. 85 and NA0. 65 are switched by switching incident luminous flux diameters ϕ1 and ϕ2 to an objective lens 109, the expander optical system 114 having same luminous flux diameters ϕ3 and ϕ4 (ϕ3=ϕ4) at incidence of the expander optical system 114 between the two media of luminous fluxes passing through ϕ1 and ϕ2 is adopted. The expander optical system 114 is used to make light utilization efficiency and RIM strength equal in the case of the optical recording medium (BD) and the optical recording medium (HD). <P>COPYRIGHT: (C)2007,JPO&INPIT |
